Drafting instrument



May 1, 1951 H. ANDEREGG 2,551,082

DRAFTING INSTRUMENT Filed Aug. 11, 195o Bnventor HEP/714 /V/V /VEQEGG Patented May 1, 1951 DRAFTING INSTRUMENT Hermann Anderegg, Malakoff, France, assignor to La Cellophane, Paris, France, a French com- Application August 11, 1950, Serial No. 178,845 In France June 2, 1947 Z Claims.

This invention relates to drafting instruments and more particularly to ruling devices mounted for parallel motion over the surface of the drawing board.

Drafting instruments of this character, whethervof parallelograms orband type, generally include a forearm supporting the head of the instrument, which is fitted with the right-angled rules, linked to another arm which in turn swings around fan anchoring means attached to the drawing board. K y l v When the drawing boardis inclined, the as- Asembly described above tends to fall of its own weight towardsY the, foot ofthe board. It is therefore desirable to balance drafting instruments intended for. Work at a `certain inclination in such a manner that the draftsman can, without appreciable effort, displace the head over the entire surface of the board, and that this head will remain at a point where it has been placed without tending to shift when re-released. The present invention accomplishes this purpose in a simple and improved manner.

This application is a continuation-in-part of my co-pending application Serial No. 109,285 led August 9, 1949, for Drafting Instrument.

In the drawing the figure is a plan view of a drafting instrument embodying the present invention.

This device is shown for purposes of illustration as applied to a parallelogram type instrument. However it is equally applicable to a band instrument.

In the figure a drawing board I is mounted on a suitable support and is adapted to be inclined in any position from horizontal to vertical. An anchoring bracket 2 is attached to the board and carries parallelogram links t and ft which are pivoted to the bracket '2 at 5 and 5 respectively. The other ends of the links 3 and 4 are pivoted at I and 3 respectively to a block 9 to which parallelogram links lil and II are pivoted. A support i2 carrying the drafting head I3 is attached to the second parallelogram by means of links IG and II pivoted at III and I5 respectively. The drafting head I3, which is rotatable about its axis, carries a set of rules I6 and I1 set at right angles in the usual manner.

This assembly is balanced, pursuant to the present invention, in the following manner:

A steel wire 2li attached at l5 engages the 2 strument involved. It is not, however,. essential that the position of the pin 22 coincide with the center of the quadrilateral formed by the links 3 and 4 andthe block 9. The wire 20, after passing around the pulley 2l, is attached at 23 to one end of a spring 24 which in turn is attached at 25 to the frame 26-of a trolley 2l riding on a flexible rod 28 having a suitable curvature. The rod 28 is rnade` of elastically `deformable material, such as pianoV wire and is adapted to iiex in response to an excessive pull by the spring 24 which may occur in certain positions of the drafting head. The spring 24 normally balances the pull of the drafting head. In some positions, however, the spring may exert more pull than that required to balance the head and tend to pull the head upwardly. The piano wire 28 flexes in response to such pull and relieves the tension of the spring. This prevents instability of the head when the spring '24 is under such excessive tension although the rod 28 normally provides a xed path for the trolley 21.

This rod 28 is clamped to the bracket 2 by means of a screw 2B which xes its position once its curved portion has been properly oriented.

When the parallelogram links 3 and f3 are inclined to the left or to the right of the vertical X-Y, the trolley 21 is automatically displaced to the left or to the right along the curve of the rod 28, in such a manner that the axis of the spring 24 is always directed along the normal to this curve. Thus, e. g. in the dotted position of the first parallelogram in the figure, the trolley 21 has moved to the position 21.

The tension of the spring, represented by the vector OR, may be resolved into two components OM and ON.

The component OM applied to the block 9 is without effect, being directed towards the points 5 and 6, whereas the component ON applied to the block 9 counterbalances the eifect of the weight of the parallelogram links 3 and 4, the block 9, and the parts carried thereby.

The action would be the same for a position of the parallelogram links 3 and II to the left of the vertical, the trolley 2l then passing to the leftgroove of a pulley 2l which is mounted by a g pin 2'2 on the block 9. The radius of this pulley `2| may vary according to the type of inhand part of the rod 28.

The parallelogram links In and II and head I3 likewise tend to fall of their own weight. The wire 20 exertsa force represented by the vector OR upon the point I5 and this may be resolved into its two components OM' and ON. The latter opposes the effect of gravity upon the head I3 and the parts carried thereby.

The explanation just given of the modus operandi of the spring is intended solely to convey an understanding of its counteractive effect against gravity, but a thorough stress analysis would show that in the various positions which the instrument may occupy on the surface of the board, a balance is obtained which, while not perfect, is amply sufficient for practical purposes.

The spring may be fitted with a simple and known device with which it is possible, for a given inclination of the board, to obtain a suitable tension relative to that inclination.

The arrangement which has beenY described may of course, without transcending the scope of the invention, be adapted to the various known forms of jointed drafting instruments.

It will be noted in particular that the device described has a single spring for balancing the two arms. However, it would notV be beyond the scope of the present invention to modify the same by'limiting the action of 'the spring 24 to the balancing of the upper arm, attaching it to a fixed point on the block 9, and accomplishing the balancing of the lower arm by means of an independent spring attached to another fixed point on the block 9.'

The system described is simple, and practical, and is suited to commercial use.

What is claimed is:

1. A drawing board having an instrument mounted on a member to swing with a parallel motion over the surface of the board, and a spring attached at one end to said member and adapted to exert a pull for balancing the weight of said member, an anchor for the other end of said spring and a curved exible wire track supporting said anchor for movement along a normally xed path in response to the swinging of saidmember, said path being selected to cause the spring to oppose the effect of gravity in all positions of said member, said wire being deformable in response to an excessive pull of said spring caused by said member when in certain positions.

2. In a drawing board, a pair of parallelogram links pivoted to swing thereover and carrying a block, a second pair of parallelogram links pivoted to said block and carrying a drafting head, a pulley on said block, a flexible tension member attached to said head and extending around said pulley, said tension member being adapted to exert a pull for balancing the weight of said head a trolley attached to the free end of said tension member, a flexible wire supporting said trolley for movement along a normally fixed path in response to the swinging of said block, said path being selected to cause said tension member to oppose the effect of gravity in all positions of said head and being deformable in response to an excessive pull of said tension member caused by said head when in certain positions.

HERMANN ANDEREGG.

REFERENCES CITED The following references are of record in the le of this patent:

FOREIGN PATENTS Number Country Date 175,183 Great Britain Feb. 16, 1922 411,243 Great Britain June '7, 1934 551,532 Germany July 9, 1932` 

